1. Field of the Invention
The present invention concerns a metal nitride oxide semiconductor device capable of use as a memory element. More particularly the invention concerns such a semiconductor device wherein a more heavily doped region of the same type as the substrate is provided under the channel of the normally depletion mode device, which region permits conversion of the device to an enhancement mode state whereby storage of information is possible therein.
2. Description of the Prior Art
With the development of a new type of semiconductor device referred to as a metal nitride oxide semiconductor it has been recognized that the MNOS device exhibits a capability of storing charge in the oxide nitride interface of the gate region thereby tending to vary the threshold voltage of the device. Consequently it has been recognized that such devices have utility for use as memory elements. One particular advantage of memory elements fabricated of MNOS devices is that they are extremely non-volatile. Consequently it is not necessary to continually refresh the information stored within the device.
For example, U.S. Pat. Nos. 3,549,911; 3,702,466; and 3,719,866 describe MNOS semiconductor devices utilized in various configurations as memory elements. These patents are believed to describe typical applications of MNOS devices in the art. However, it should be recognized that a continuing need exists for improved metal nitride oxide semiconductor devices which can be operated with relatively low voltages and which are simple to fabricate.